Storage tube



Nov. 26, 1968 c. GUILLARD ETAL 3,413,514

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av non" United States Patent 3,413,514 STORAGE TUBE Claude Guillard, Georges Morillot, and Georges Sud, Paris, France, assignors to CSF-Compagnie Generale de Telegraphic Sans Fil, Paris, France Filed Jan. 28, 1965, Ser. No. 428,634 Claims priority, application France, Feb. 4, 1964, 962,555 14 Claims. (Cl. 315-12) ABSTRACT OF THE DISCLOSURE An image analyzing storage tube wherein a rectangular picture is inscribed upon a circular target the surface of which is only in part occupied by the picture, and having a plane secondary electron collector in front of the target. In that case a shading effect arises in the picture, and the V invention corrects this effect by uniformizing the rest current in the target, especially by introducing in the structure of the collector and/or its neighbouring electrodes some modifications of geometrical and/or electrical nature, in view of establishing a dissymmetry in the structure.

The present invention relates to image-analyzing storage tubes in which the signal is inscribed in the form of a charge pattern on the surface of an insulating target charged by the inscription electrons, this target being thereupon discharged in the course of scanning by a reading beam whose electrons have such a velocity that the insulating surface emits several secondary electrons for a primary impact electron (secondary emission coefiicient 1), the signal being finally collected on a collector of at least a part of these secondary electrons.

The present invention relates more particularly to tubes of this type in which the scanned area occupies only a portion of the insulating surface, as is the case with the circular targets scanned according to television standards (scanning in two rectangular directions, rectangular format, ratio of the sides of the rectangle 4:3, the diagonal at the most equal to the diameter of the target).

Accordingly, it is an object of the present invention to provide a storage tube of the type described hereinabove which is simple in construction and effectively eliminates the shortcomings encountered with the prior art constructions, particularly as regards the shading eiiect encountered therewith.

Another object of the present invention resides in the provision of image-analyzing storage tubes in which the image at rest, that is without signal, is uniformly brilliant.

A further object of the present invention resides in image-analyzing storage tubes, especially for television and the like, in which the definition of the tube is maintained relatively high and parasitic modulation signals are substantially eliminated.

A still further object of the present invention resides in the provision of a storage tube for analyzing images which at least considerably minimizes, by extremely simple and inexpensive means, the objectionable shading effects encountered heretofore with the prior art constructions.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein:

FIG. 1 is an explanatory diagram in which the current intensity i is plotted against vertical image coordinates y.

FIG. 2 is a plan view of a target assembly of the prior art.

FIG. '3 is an axial cross-sectional view through the prior art target of FIG. 2.

FIG. 4 is a plan view of a modified collector according to the present invention.

FIG. 5 is an axial cross-sectional view of the target and collector assembly of FIG. 4 with the addition of an auxiliary electrode in accordance with the present invention.

FIG. 6 is an axial cross-sectional view through a modified embodiment ofa target and collector assembly according to FIG. 4 with the addition of a conductive deposit on the target.

FIG. 7 is a plan view of a modified collector, similar to FIG. 4, in accordance with the present invention, cut into several electrically separated sectors.

FIG. 8 is an axial cross-sectional view through a still further modified embodiment of a target and collector assembly, similar to FIG. 4, with the collector thereof in an inclined position with respect to the target.

FIG. 9 is an axial cross-sectional view through still another modified embodiment of a target-collector assembly in accordance with the present invention, and

FIG. 10 is a perspective view of the collector of FIG. 9, similar to FIG. 4 but modified by the addition of an auxiliary part approaching the target.

It is known that for the proper operation of these types of tubes, particularly to obtain at the reception an image during rest (i.e., without signal), which is uniformly brilliant, it is desirable that the rest potential of the target be uniform at all points of its surface. This uniformity will translate itself by a straight horizontal line on the diagram representing the current intensity on the collector as a function of time, and therefore also in the diagram representing the same current intensity as a function of the vertical coordinate of the image (the vertical scanning or frame scanning being linear as a function of time). This straight line is indicated at A in the diagram of FIG. 1 whose .abscissae are graduated in vertical image coordi nate y and whose ordinates are graduated in collector current intensity 1.

The best means to obtain such a uniformity would be to realize the collector in the form of a plain plate parallel to the insulating surface of the target. However, these means are not practicable, for it is necessary that this plate permits the passage of the reading electron beam. This form of the collector can therefore be realized only in the form of a grid. Such a grid absorbs, however, a portion of the reading beam, the more the smaller its transparency; it additionally gives rise to a parasitic modulation signal which diminishes the definition of the tube. These defects have lead to a search for the realization of the collector either in the form of a hollow cylinder with walls perpendicular to the target or in the form of a plate parallel to the target and pierced with a circular orifice, the internal diameter of the cylinder or the diameter of the orifice being at least equal to the diagonal of the image. This arrangement is represented in FIG. 2 where reference numeral 1 designates the rectangular scanned area, and reference numeral 2 designates the annular collector pierced with a circular orifice 3 whose rim 4 coincides in this projection with the contour of the target 5, visible in FIG. 3. In this latter figure, one has also schematically indicated by the arrow 6 the reading beam.

The experience has demonstrated that with this arrangement of the prior art, the rest current is no longer represented by the straight line A of FIG. 1, but by the curve B whose ordinates are larger than that of the straight line A at the beginning of the scanning (at the top of the image) but decrease below the straight line A toward the end of the scanning (at the bottom of the image). A shading results therefrom at the reception, impairing the rest image, which is more brilliant at the top and becomes less and less brilliant in descending, to terminate 3 by a black band at the bottom. The same defect, though to a lesser degree, affects the image in the horizontal direction.

Research of applicants have established (it being understood that the essence of the present invention described herein does not depend on the correctness of this theory) that this defect appears to be due to the superposition of two effects:

(a) Effect of the existence on the target of areas not scanned by the beam (segments of the circle comprised between the circumference 4 and the rims of the area 1 in FIG. 2); if this effect existed alone, the potential distribution at rest on the target would be such that the rest current as a function of the coordinate y would have the shape of the curve C in FIG. 1.

(b) Effect of the dissymmetry of scanning (saw-tooth form), effect which would translate itself by the fact that those of the secondary electrons emitted by the target which fall back on its surface, fall back in preferential manner on the surface already scanned by the beam in the course of a given exploration (surface above the line scanned at a given moment) While a relatively small quantity falls back on the portion of the area not yet scanned. Owing to this redistribution, the rest potential is modified in such a manner that, if this effect existed alone, the collector current as a function of the coordinate y would follow the substantially rectilinear curve D of FIG. 1.

The curve B is precisely the arithmetic sum of the curves C and D.

According to the present invention, one makes in the collector structural modifications susceptible to eliminate these effects and to render substantially uniform the rest current by bringing the same back substantially to the straight line A of FIG 1.

These modifications act conjointly in the desired sense but are of different nature, depending on whether one acts against one or the other of the effects (a) and (b) mentioned above:

(1) The effect (a) (nonscanned segments adjacent the rims of the image) is reduced by extending the metallic surface of the collector in such a manner as to extend above these segments. This comes back to replacing the circular aperture of known type by an aperture corresponding to the format of the image, particularly by the rectangular aperture 7 in the collector 2 of FIG. 4, the dimensions of the aperture corresponding to the area 1 of FIG. 2.

This arrangement may be advantageously combined with a correction electrode 8, provided with a similar aperture 9, disposed between the collector 2 and the target and carried at a suitable potential (FIG. 5), or with a conductive deposit 10 on the surface of the surface of the target 5, this deposit delimiting the area to be scanned (FIG. 6). All of these arrangements have for effect to render uniform the electrical field between each point of the involved segments and the metal of the collector, the lines of force becoming straight and perpendicular to the target also within the limits of these segments.

(2) The effect (b) (the dissymmetry of the scanning) is compensated by a dissymmetry introduced into the collector, this dissymmetry being either electrical or geometric.

The electrical dissymmetry may be introduced by dividing a collector into several sectors galvanically or electrically separated, for example, into four sectors 11, 12, 13 and 14, and by carrying the sectors at different potentials suitably chosen (FIG. 7).

According to a modification, the electrical dissymmetry may be introduced by realizing the collector 2 of FIG. 2 or FIG. 4 of resistive material, and by causing the same to be traversed by a current whose imput and output are located at diametrically opposite points 21 and 22 of the axis parallel to the coordinate y of the image,

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in such a manner that the circulation of this current will produce in the collector a variable potential from one point to the next.

The geometric dissymmetry may be introduced by decreasing the distance between the target and the metal of the collector on the side of the rim of the aperture corresponding to the bottom of the image, with respect to the rim of the opposite side. This approachment may be made either by inclining the collector at a certain angle, to be experimentally determined (for example, by an angle a=15 to 20) between the plane of the collector and the plane of the target 8 (FIG. 8) or by fixing to the rim of the aperture 7, facing the lower rim of the area 1, a sheet metal piece 15 folded into an angle iron as shown in cross-section in FIG. 9 and in perspective view in FIG. 10. As an example, favorable results were obtained with distances d=15 mm. and d'=4 mm. (FIG. 9), for the width of the aperture 7 s=30 mm.

While we have shown and described several embodiments in accordance with the present invention it is obvious that the same is not limited thereto but is susceptible of numerous changes and modifications as known to persons skilled in the art. For example, the various arrangements described herein may be combined and interchanged with one another.

Applicants have established that by the applications of these diverse means, it has been possible to obtain for a given target a characteristic i=f(y) according to the curve B of FIG. 1, that is, extremely close to the ideal straight line A.

Thus, it is obvious that the present invention is not limited to the details shown and described herein but is susceptible of numerous changes and modifications as known to persons skilled in the art and we therefore do not wish to be limited to the details shown and described but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting frame scanning, source means for producing a beam of said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signal.

2. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting line scanning, while the other coordinate constitutes frame scanning, source means for producing a beam of said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signals, the active area covered by said scanning being a portion of the entire area of said target, and the shading eliminating means including means for masking by plain parts of said planar electrode the differential area portions between the area of said target and said actively scanned area.

3. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting line scanning, while the other coordinate constitutes frame scanning, source means for producing a beam of said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signals, said aperture having substantially the same shape and size as the said active area covered by said scanning on said target.

4. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting line scanning, while the other coordinate constitutes frame electrons, and secondary electron collector means said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means providing a dissymmetry for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signals.

5. The combination according to claim 4, wherein said dissymmetry is mechanical in nature.

6. The combination according to claim 4, wherein said dissymmetry is effectively formed at least in part by an inclination of said planar electrode with respect to the target surface.

7. The combination according to claim 6, wherein the angle of inclination is about to 8. The combination according to claim 4, wherein said dissymmetry is effectively formed at least in part by a metallic piece fixed substantially to the edge of said aperture near the end of the frame scanning, said piece eX- tending into the space between said planar electrode and said target.

9. The combination according to claim 8, wherein said piece is an angularly bent sheet.

10. The combination according to claim 4, wherein said dissymmetry is electrical in nature.

11. The combination according to claim 4, wherein said dissymmetry is effectively formed at least in part by said planar electrode of relatively resistive material, and means for passing an electric current through said electrode approximately in the direction of said frame scanning.

12. The combination according to claim 4, wherein said dissymmetry is effectively formed at least in part by said planar electrode divided into a plurality of electrically separated parts, and means for applying different electric potentials to different ones of said parts.

13. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting line scanning, while the other coordinate constitutes frame scanning, source means for producing a beam of said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signals, and correcting electrode means between said planar electrode and said target, said correcting electrode means having an aperture of substantially the same shape and size as the aperture in said planar electrode, and both apertures being in substantial alignment.

14. In a storage tube having a target with an insulating layer for storing modulated signals and means for scanning the surfaces of said layer with electrons of such a velocity that the secondary emission factor of the said surface is greater than unity, the scanning means being operative to scan said surface along two angularly displaced coordinates, one of the coordinates constituting line scanning, while the other coordinate constitutes frame scanning, source means for producing a beam of said electrons, and secondary electron collector means in the form of a substantially planar electrode located between said source means and said target and having an aperture for passing therethrough said beam, said planar electrode including means for substantially eliminating the shading appearing progressively in the secondary electron distribution on the target surface in the direction of said frame scanning in the absence of modulation on said signals, and a conductive coating applied on the surface of said target and forming a frame for said active area.

References Cited UNITED STATES PATENTS 3,086,138 4/1963 Hendry 315-11 3,115,592 12/1963 Scott et a1. 315-12 RICHARD A. FARLEY, Primary Examiner.

J. P. MORRIS, Assistant Examiner. 

